Slots in fan housing to reduce tonal noise

ABSTRACT

A fan housing is provided with slots formed in the enclosure of the fan housing. The slots are sized appropriately to filter the noise generated during operation of the cooling fan; e.g., tonal noise produced by the rotation of the blades. The slots may either be vented to the outside of the enclosure or closed off.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority from U.S. ProvisionalApplication No. 60/755,743, filed Dec. 29, 2005, and is fullyincorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to cooling fans and in particular to a fanhousing configured to reduce noise in a cooling fan.

The prior art for fans includes a housing and a fan assembly. The fanassembly fits into an air passage region provided in the housing. Thefan assembly includes an impeller unit and a motor for driving theimpeller unit. The housing typically comprises a base to which the motoris attached and an enclosure (or casing).

A common problem with fans is the noise they generate during operation.A particularly displeasing noise component is tonal noise. Tonal noiseis a result of the rotation of the fan blades. The frequency spectrum oftonal noise comprises largely of components (fundamental and harmonics)of the blade passing frequency, which is the number of fan blades timesthe shaft speed (revolutions per second). Broadband noise is anothernoise component, but is less noticeable as compared to tonal noise sinceits frequency spectrum is generally much broader that the frequencyspectrum of tonal noise and the amplitudes of its frequency componentsare lower.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provide a fan housing having slotsin the enclosure (casing) of the fan housing. The slots are sizedappropriately to filter the noise generated during operation of thecooling fan; e.g., tonal noise produced by the rotation of the blades.The slots may either be vented to the outside of the casing or closedoff.

Sizing the width of the slots to match with the frequencies of the noiseis an important consideration. Typically, a larger number of slots (slotcount) is preferred (limited by manufacturing costs), and smaller sizedslot widths are preferred (also limited by manufacturing costs).Generally, the dimensions of the slot (volume, area, etc.) and slotcount are dependent on the blade passing frequency.

In one embodiment, the slots are provided in the corner regions of thefan housing enclosure. In other embodiments, the slots may be filledwith sound-absorbing material.

Additional noise reduction can be achieved by providing noisesuppression. For example, the corner regions can be provided withnoise-suppressing devices or materials to interact with noise due torotation of the blades to weaken and/or cancel the noise. The cornerscan be constructed of noise absorbent material.

Studies have shown substantial reduction in noise during fan operationwith no adverse affects in fan performance such as pressure and flow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 1A illustrate a fan and fan housing according to the presentinvention.

FIGS. 2A and 2B illustrate top cutaway views of a fan housing accordingto the present invention.

FIGS. 3A to 3C illustrate variations in slot design according to variousembodiments of the present invention.

FIGS. 4A to 4C illustrate views of the slot openings formed through theinterior surface of the enclosure of the fan housing.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a perspective view of a cooling fan according to anillustrative embodiment of the present invention. A fan housing 102houses an impeller unit 104 which includes a set of fan blades 112connected to a hub 114. The hub 114 houses a fan motor (not shown). FIG.1A shows the fan housing 102 without the impeller unit. The fan housing102 comprises an enclosure (casing) 122 which encloses the fan blades.The fan motor is supported on a supporting base 124 of the fan housing102. An axle bearing 126 provided on the supporting base 124 provides abearing surface on which a rotor component of the fan motor rotates. Thesupporting base 124 is connected to the enclosure 122 via connectingstruts 128.

In the illustrative embodiment of the fan housing 102 shown in FIGS. 1and 1A, the enclosure 122 is provided with vertically oriented features132 which are slotted openings formed through the interior surface ofthe enclosure. In the embodiment shown, these vertically orientedfeatures are vertical slots provided through the interior surface of theenclosure 122.

In FIG. 1, the slots 132 are exposed to the exterior of the enclosure122. However, it was shown through experimentation that forming slots(see FIG. 2, for example) which did not pass through the exteriorsurface of the casing provided improved noise reduction. Nonetheless,slots which are vented to the outside of the enclosure can provide somenoise reduction.

In the particular embodiment shown in FIG. 1, a set of slots 132 areprovided in each of the corner regions 142-148 of a rectilinear housing102. However, in other embodiments, fewer than all of the corners can beprovided with vertical slots. For example, a fan according to oneembodiment of the present invention may comprise a housing enclosure inwhich diagonally opposed corners (e.g., 142, 146) are provided withslots. A fan according to another embodiment of the present inventionmay comprise a housing enclosure in which an adjacent pair of cornersare provided with slots (e.g., 142, 144). In accordance with anotherembodiment, slots may be provided in only one corner of the housingenclosure.

In still other embodiments, the slots can be provided on the interiorsurface along the side regions of the enclosure. For example, thehousing 102 shown in FIG. 1 is rectilinear. For a circular-shapedhousing, there are no “corner regions;” however, the slots cannonetheless be provided through the interior surface of the enclosure.

FIG. 1A illustrates an embodiment in which the slots are closed off formthe exterior. Here, the slots are shown in phantom to indicated thatthey do not penetrate through the exterior surface of the casing(enclosure) 122.

The schematic drawing of FIG. 2A illustrates an example of such anembodiment. The figure is a cutaway view of an enclosure 222 of a fanhousing viewed from the top. The figure shows the air passage region 224within which an impeller unit is disposed and within which the fanblades of the impeller unit rotate causing air to flow through the airpassage. The interior surface of the enclosure 222 defines the airpassage region 224. Fins 234 formed within the interior surface of theenclosure define slots 232 which is the spacing between fins.

Slots 232 are defined as the space between fins, and the dimensions andshapes of the slots are defined by the dimensions and shapes of the fins234 and the spacing between the fins. In one embodiment, the size andspacing of all slots 232 may be uniform. However, it will be understoodthat the slot dimensions and shape may vary so that the slots are notuniformly formed or spaced.

The embodiment of FIG. 2A shows a set of slots formed in side regions ofthe interior of the enclosure 222, rather than at the corner regions.Fins 234 are formed on the interior surface of the enclosure. In oneembodiment, the fins are formed from the material of the enclosure; forexample by casting. Alternative embodiments include only one set ofslots formed on one side region; one set of slots formed on one side andanother set of slots formed on an opposing side or on an adjacent side;slots formed in the corner regions and in the side regions.

FIG. 2A further illustrates that the slots 232 are not formed throughthe enclosure 222 to the exterior of the enclosure (similar to FIG. 1A),the slots are closed off from the exterior. This was shown to providegreater noise reduction than if the slots were formed through theenclosure as illustrated by the embodiment shown in FIG. 1.

The slots 232 can be filled with noise reduction material 242 (e.g.,foam, cotton batting). FIG. 2B illustrates this aspect of the presentinvention. The noise reduction material 242 can be provided in each slot232, or in some of the slots. The noise reduction material can fullyfill a slot, or can partially fill a slot. An alternative to the use ofnoise reduction material is the formation of a web-like structure withinthe slots 232 which act to dissipate the noise. Furthermore, the regionsin the corner may house noise suppressing material (e.g., foam, cotton)or devices for further noise reduction.

The fins 234 may be formed of the same material as the enclosure. Thiswould be advantageous from the point of view of manufacturing where thefan housing can be cast in a single step from a die by injectionmolding. Alternatively, the material for the fins 234 may be differentfrom that used to produce the fan housing. This would allow for the useof sound absorbent material to improve noise reduction. In addition, anoise absorbent material can be used to construct or manufacture thecorner portions of the housing, or the noise absorbent material can beembedded in the corner portions. Typical noise absorbent materialsinclude cotton batting, foam, and the like.

Still other embodiments include a combination of FIGS. 1 and 2, whereslots can be provided in the corner regions and in the side regions. Anadditional benefit of having additional slots is to further reduce theweight of the cooling fan.

FIGS. 3A-3C show alternative configurations of slots in accordance withthe present invention. The view is a cutaway top view of an enclosure322 of a fan housing, looking down. A portion of the air passage region324 is shown to provide perspective. The slots 332 may formed into thematerial of the fan housing in a radial direction, or slanted toward oragainst the direction of rotation, or some combination thereof. In FIG.3A, the slots 332 are formed into the material and are substantiallyequally spaced and arranged in substantially parallel fashion. In FIG.3B, the slots 332 are formed to face into the direction of rotation ofthe fan blades as indicated by the arrow.

In FIG. 3C, the slots 332 have varying width and in particular a varyingincreasing width (also a decreasing width is possible). In the exampleshown in FIG. 3C, the slots 332 become wider as one moves away from theblade region (i.e., the air passage region). FIG. 3C shows a magnifiedportion illustrating the slot widths w₁, w₂, w₃ to be increasing in astepped fashion. However, in another embodiment the slots can have asloped shape (not shown). By increasing the slot width, zones ofexpansion are created which contribute to the reduction of the noise.

The slots illustrated in FIGS. 1, 1A, 2A, and 2B show substantiallyvertically oriented slot openings. It is noted, however, that the slotopenings need not be vertical. FIG. 4A shows a portion of the enclosure422 of a fan housing. The figure illustrates a head on view of the slots432 formed into the interior surface of the enclosure 422, viewed fromwithin the air passage region of the enclosure. The figure shows thefins 434 are substantially vertically oriented (i.e., parallel to theaxis of rotation of the fan blades) and in parallel relation to eachother. The slot openings 402 are thus vertical. The embodimentillustrated in FIG. 4B shows a configuration where the fins 434 areslanted relative to the axis of rotation, resulting in slot openings402′ that are slanted relative to the axis of rotation. In yet anotherconfiguration, the fins 434 may be arranged in a combination of verticaland slanted (slanted right, or slanted left) orientations so that theslot openings are similarly oriented.

The foregoing embodiments show that the slots extend from the topsurface of the enclosure to the bottom surface of the enclosure. Theembodiment shown in FIG. 4C shows a variation of the slots. Here, slotopenings 402′ do not extend the full length from the top surface of theenclosure 422 to the bottom surface of the enclosure. These slots can beformed by drilling through (or otherwise piercing) the interior surfaceof the enclosure 422 into the material of the enclosure. Alternatively,the slots can be pre-formed by casting them into a top half of the fanhousing and into a bottom half of the fan housing, and attachingtogether the two halves. The figure shows slot openings 402′ are formedat an angle (slanted); however, in another embodiment, the slottedopenings may be substantially vertical. This construction provides for amore rigid fan housing structure which may be a desirable feature forcertain fan applications. Though not shown, the slotted openings canextend through either the top surface or bottom surface of the fanhousing, but not through the other surface.

The selection of slot dimensions such as the cross-sectional area of theslot and the slot volume, should include consideration of the bladepassing frequency and its higher harmonics. The particular combinationof the slot's cross-sectional area and volume affect the acoustic wavesfrom the noise of the blades as they travel into the slots and give riseto a unique set of frequencies that interact with all other frequencies,including the blade passing frequency and its higher harmonics to reduceoverall tonal noise. The acoustic frequency components produced by theslots weaken the fundament frequency (blade passing frequency) andhigher harmonics.

As described above, the corner regions of the fan housing can beutilized to provide noise suppression means. One such means is toincorporate devices in the volume of space in the corner regions of thefan housing, which are is typically available and unused. For example,small speaker components can be disposed in some of the corner regionsand operated in accordance with acoustic cancellation techniques. Aproperly position microphone (or microphones) can pick up the fan noise.Cancellation software can drive the speakers to provide noisecancellation. Other “devices” might include the use of sound absorbingmaterial in the construction of the fan housing.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

1. A fan comprising: a fan housing; an impeller unit disposed within thefan housing; and a fan motor disposed within the impeller unit, the fanhousing having an interior circumferential surface, the fan housingfurther having fins formed in the material of the fan housing throughthe interior circumferential surface thereof, wherein the fins defineslots therebetween, wherein the width of at least one of the slottedopenings varies in a stepped fashion.
 2. The fan of claim 1 wherein thefins define slots therebetween, wherein slotted openings are formedthrough the interior circumferential surface.
 3. The fan of claim 2wherein the slotted openings extend through at least a first majorsurface of the fan housing or a second major surface of the fan housing.4. The fan of claim 2 wherein the extent of the slotted openings doesnot reach a top surface of the fan housing nor a bottom surface of thefan housing.
 5. The fan of claim 1 wherein the fins are oriented insubstantially parallel relation to axis of rotation.
 6. The fan of claim1 wherein the fins are slanted relative to the axis of rotation.
 7. Thefan of claim 1 wherein at least some of the fins are slanted eitheragainst the direction of rotation of the fan blades of the impeller unitor in the direction of rotation of the fan blades of the impeller unit.8. The fan of claim 1 wherein the fan housing is rectilinear and thefins are disposed in corner portions of the rectilinear housing.
 9. Thefan of claim 8 wherein the material is a sound absorbent material,including cotton, a rubber-like material, or a foam material.
 10. Thefan of claim 1 wherein the fan casing is rectilinear and the fins aredisposed in surface regions between corner portions of the rectilinearhousing.
 11. The fan of claim 1 wherein the slotted openings do notpenetrate through the outer surface of the fan housing.
 12. The fan ofclaim 1 wherein at least some of the slots are filled with material. 13.A cooling fan comprising: a fan housing; an impeller unit disposedwithin an air passage region of the fan housing; and a fan motordisposed within the impeller unit, the fan housing having an interiorcircumferential surface, the fan housing further having slots formedinto the material of the fan housing and opening into the air passageregion through the interior circumferential surface, wherein an interiorsurface of a first slot has a stepped profile.
 14. The fan of claim 13wherein the slots extend through both a first major surface of the fanhousing to a second major surface of the fan housing.
 15. The fan ofclaim 13 wherein the slots extend through a first major surface of thefan housing and not through a second major surface of the fan housing.16. The fan of claim 13 wherein at least some of the slots are filledwith material.
 17. The fan of claim 16 wherein the material is a soundabsorbent material or a cotton material or a foam material.
 18. The fanof claim 13 wherein at least one of the slots is disposed in a cornerregion of the fan housing or in a side region of the fan housing.